Quote:
Originally Posted by Humptydumpty
David this 40 uf is that the overall total , or 120 uf total uf of the can . On the can it reads 40-40-40 So is there any one that would rebuild these caps. I did a search when i started to work on the receiver to replace the cap , and i came up with nothing . Lots on youtube but not step by step on how it is done .
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There are three separate capacitors in the can, which is why it states 40-40-40. We tend to call them 'smoothing capacitors' for shorthand, but the first one after the rectifier is strictly speaking, the 'reservoir' capacitor. On your set, they are C40, C41 & C42. I've highlighted them on the clip of the circuit below.
The role of the reservoir capacitor is to smooth out the ripple that remains after the AC voltage has been rectified. The smoothing capacitor(s) provide additional smoothing. If the capacitors deteriorate over time, as they do, they fail to reduce the ripple. In a half-wave rectified power supply this presents as 50 Hz hum, and in a full wave rectified supply, as 100Hz hum.
It might help you to understand how smoothing circuits work if you look at the sketches below, which cover half-wave and full wave rectification.
To check if the three capacitors in the can are causing the hum, it would be necessary to disconnect the positive connection(s) of each section in turn and to temporarily wire a replacement capacitor, (which would need to 47µF as 40 µF is an obsolete value), from the wires that were connected to the positive tag of the original can, and ground. If that does indeed cure the hum (remembering that in any event, the 9R59DS is noted for some background hum), then it would be a choice of either permanently and safely wiring the three external capacitors under the chassis, leaving the can disconnected but in place, though more experienced restorers (rather than 'repairers'), might opt to open the can, remove the contents, fit three compact capacitors in the can and re-seal it. Any replacements will need to have at least the same working voltage as the originals.
The last picture shows examples of modern compact capacitors with adequate ripple ratings, which will fit side by side inside typical smoothing cans.
You've done well to get as far as you have with the support of others, but without wishing to sound unkind, I don't think you have the competence or experience to safely undertake any of the tests or repairs on the power supply and would be better advised to entrust the work to someone else - for example from the 'Services Offered' section of the forum - (or maybe attend one of the 'workshops' that are arranged from time to time by various individuals). The work involves some live testing, an ability to understand how the circuit relates to the components on the chassis, and an awareness that even when a set is disconnected from the mains, high voltage smoothing capacitors, if not discharged, can hold a charge for some time and cause nasty shocks to the unwary.
I think that's as much help and advice as I feel able to give.